This invention concerns an improved ruthenium-catalyzed process for dimerizing alkyl acrylates to dialkyl hexenedioates. The latter compounds are readily convertible to adipic acid (hexanedioic acid) by hydrogenation and subsequent hydrolysis. Adipic acid is used to produce condensation polymers such as nylon 66.
Alderson, U.S. Pat. No. 3,013,066, and Alderson, Jenner, and Lindsey, J. Am. Chem. Soc., 87, 5638 (1965), disclose the reaction of methyl acrylate in the presence of ruthenium chloride and methanol to give a mixture of products that includes dimethyl 2-hexenedioate.
Can. Pat. No. 796,775 discloses the dimerization of alkyl acrylates in the presence of a mixed ruthenium compound-zinc catalyst, a hydrogen donor, and a phosphine. This patent is discussed in more detail in connection with Examples M, N and 67 just preceding the claims.